Plato, Phaedo 79 (DIORISIS sentence 508)

οὐκοῦν τούτων μὲν κἂν ἅψαιο κἂν ἴδοις κἂν ταῖς ἄλλαις αἰσθήσεσιν αἴσθοιο, τῶν δὲ κατὰ ταὐτὰ ἐχόντων οὐκ ἔστιν ὅτῳ ποτʼ ἂν ἄλλῳ ἐπιλάβοιο ἢ τῷ τῆς διανοίας λογισμῷ, ἀλλʼ ἔστιν ἀιδῆ τὰ τοιαῦτα καὶ οὐχ ὁρατά;